One issue with aircraft brake discs made from carbon is that they are prone to suffering from oxidation based on their operating environments. One attempt to protect these brake discs from oxidation involves the use of an anti-oxidant system. Anti-oxidant systems are utilized in brake discs to inhibit both catalytic oxidation and thermal oxidation.
Known anti-oxidant systems include compositions of varying components. These anti-oxidant systems have weaknesses of not addressing the issue of catalytic induced oxidation from runway deicers. The industry is ceasing to use urea deicers for environmental concerns. Instead, potassium and sodium based products are now being utilized. However, both are prone to result in catalytic oxidation of carbon brakes.
Oxidation has a negative effect on brake disc strength. In some cases, the disc may weaken to a point where it is no longer able to transfer torque, resulting in drive tenon failure. Oxidation includes both thermal oxidation and catalytic oxidation.
Thermal oxidation is experienced less frequently, but occurs due to high brake temperatures. Catalytic oxidation occurs due to the combination of chemical contamination and heat. Catalytic oxidation can occur because of cleaning fluid contamination. It has occurred more frequently after the introduction of the new generation runway deicing fluids (RDF's) based on alkali metals, acetate, and formates. Operators with route structures, where the brakes come into contact with these chemicals, experience more occurrences of catalytic oxidation. The effects of oxidation are not always immediately apparent, as the disc must be subject to elevated temperature for a certain time in order for the oxidation to fully develop.
There are growing concerns across the industry regarding the effect of RDF's on carbon brakes, particularly with respect to oxidation. The EASA and FAA have informed operators about the effects of oxidation and have suggested that carbon brake discs be inspected for signs of oxidation.
Thus, a need in the art exists for an improved carbon anti-oxidant coating for application on a carbon brake disc. An aspect of the present invention advances the art by providing an anti-oxidant coating and a carbon brake disc having an anti-oxidant coating that offer improved properties. Another aspect of the present invention also provides an improved primer coat composition.